Stage plug



` July 22, 1947.` J. H. I YTGENS STAGE PLUG Filed March 20, 1945 MIL Patented July 22, 1947 UNITED STATES PATENT OFFICE STAGE PLUG Julius H. Lytgens, Los Angeles, Calif.

Application March 20, 1945, Serial No. 583,699

(Cl. 20G-115.5)

1 Claim. 1

My invention relates to stage plugs, with particular reference to plugs employed for making electrical connections on stages, motion picture sets and the like.

In the production of stage plays and motion pictures, it is the usual practice t employ a relatively great number of portable lights for illuminating the stage or motion picture set, necessitating the use oi relatively long cables extending between the permanent Wiring system of the stage to the portable lights and necessitating the employment of readily disconnectible connectors, one for each of the lights to be employed.

In the manipulation of the stage settings and the lights, it is necessary to frequently disconnect and reconnect any particular lamp, and for this purpose it is common to employ an electrical outlet or receptacle into which an electrical connecting plug secured to the end of the cable may be inserted bearing contact terminals adapted to make contact with electrical contact terminals stationarily disposed Within the receptacle.

One form of such stage plug comprises a relatively thin strip of fibre or other insulating material, upon the opposed .edges of which are mounted a pair of metal strips constituting the contact terminals of the plug. The cables which are employed usually comprise a two conductor cable having external insulation surrounding the pair of conductors, together with fabric or other material to lend'tensile strength to the cable, each of the individual conductors having its own individual insulation such that the outer sheath of insulation may be stripped back to expose the two individual insulated conductors and to permit their individual connection to the Contact terminals on the plug. Usually the outer sheath is stripped back only a portion of the length of that part of the cable which will lie within the confines of the stage plug, the rearward end of the plug being formed as a handle portion by .which the electrician may grasp the plug for inserting in or withdrawing the plug from the receptacle.

At the handle end of the stage plug, the cable is necessarily exposed to sharp bending, whereby after some considerable use, the insulation becomes weak or broken, and the conductors become short circuited. This short circuit occurs at the handle portion of the plug exactly where the electrician will grasp the plug, and constitutes a dangerous hazard to the electrician, whose hands will be severely burned as a result of the short circuit while he is holding the plug in his hand.

While, of course, the xed wiring system of the stage is provided with circuit breakers, fuses and similar safety devices designed to interrupt the circuits in the event of a short circuit in any of the cables or apparatus employed upon the stage, however these safety devices are usually set for such high capacity that they do not interrupt the circuits with suicient rapidity to prevent the flashing and arcing at the plug from causing a severe burn to the hand of the electrician.

Therefore, it is an object of my invention to perfect a stage plug which is provided with a safety feature automatically disconnecting the conductors or interrupting the electric circuit in the event of a short circuit at any point in the cable circuit, especially the Vulnerable points comprised by the junction of the plug and cable, the junction of the cable and the electrical unit connected thereto and in the unit itself.

Another object of my invention is to perfect a device of the character described, wherein each individual stage plug will bear its own safety fuse, the current `carrying capacity of which will be maintained sufficiently low that the individual plug fuse will blow out upon a short circuit in the `cable and before injurious arcing can occur.

Another object of my invention is to provide a stage plug of the character set forth, wherein a small removable fuse is mounted within the Ibody of the plug connected in circuit between one of the cable conductors and one of the metal contact strips.

Other objects of my invention will be apparent from a study of the following specification, read in connection with the accompanying drawing wherein Fig. 1 is a perspective view of a stage plug constructed in accordance with my invention,

Fig. 2 is a longitudinal sectional view of the stage plug shown in Figure l.

Fig, 3 is a perspective view of a particular fuse structure which may be employed with my stage plug.

Referring to the drawings, I have illustrated a stage plug, indicated generally by the reference character l, comprising a block of fibre or other suitable insulating material. The block may be of any desired shape, though for the purpose of adapting it for inserting in a stage receptacle, I

' prefer to form the block with a rectangular cross section, the thickness of which is small as compared its width.

The forward end 2 of the block constitutes the plug portion thereof to be inserted into the stage receptacle and is provided upon each of its side edges with a metal contact strip indicated at 3 and il. lThe extreme forward end of the block is reduced in width to provide a proper end, facilitating the insertion of the plug into the receptacle, and the metal contact strips are curved or bent to conform with the varying contour of the block edges.

The contact strip 3 may be secured to the block by means of a pair of screws 5 and 6 disposed adjacent each to the ends of the strip, the screw 6 being preferably provided with an enlarged head beneath which the end of one of the conductors I may be disposed to make electrical contact be-` tween the conductor and the contact terminal 31 The other contact strip or terminal 4 is preferably bent into a shape substantially conforming with the contour of the edge of the block against which it will be disposed, the extreme narrow end of the strip as indicated at 8 being bent to extend along the front edge of the block where it is secured to the bloc-lt by means of a screw S. The outer endof the strip G is preferably loosely disposed within a slot III, formed in the edge of the block to permit some freedom of movement of the strip i to insure it of the frictional contact between the strip and the terminals in the receptacle, and spring I I (see Figure 2) may be disposed in a short bore extending into the side edge of the block and may be used to normally urge the outer end of the strip 4 away from the edge of the block, thus providing resilient contact between the opposed contact strips and the contact terminals in the receptacle into which the plug may be inserted.

The outer end portion of the block I is formed as a handle indicated at I2,fthe edges of the block being given a desired conguration to facilitate the grasping of the plug by the ngers of the electrician, by forming a portion of the edges of the handle with deep concave curves I3 and I4'.

To permit the connecting of the cable I5 to the block, I form a transverse elongated slot I'S in the outer end of the handle portion, the slot communicating with a bore I'I, extending longitudinally of the block to permit the passage of the conductors in cable I5, when the cable end is inserted in the block.

As will be apparent from an inspection of Figure 2 the bore I1 communicates with an aligned relatively large bore I8, extendingfrom the inner end of the block by way of a small passage I9 through which one of the conductors 20 extends, while a second small passage 2I extends into communication with the bore I'I from the edge of the block along. which the contact strip 3 is disposed to permit the passage of the conductor 'I into position allowing connection to the screw 6.

The enlarged bore I9 provides a housing, into which may be inserted a safety device in the form of a fuse 22, the fuse preferably having the construction of the ordinary cartridge fuse, with special terminals secured to the end caps of such cartridge fuse, this construction being illustrated particularly in Figure 3.

One of the special terminals indicated at 23 comprises a short length of relatively heavy copper or other similar metal, extending in a plane parallel to and intersecting the longitudinal axis of the cartridge fuse, the terminal 23 having a short aperture 25 formed therein in a position to be disposed in alignment with a transverse bore 25, extending from one side of the block into communication with the fuse housing bore I8, and through which a screw 26 is inserted to threadedly engage the aperture 24 to connect the end of the conductor 20 to the terminal 23. The other terminal for the fuse 22 is preferably formed as a short strip of copper or similar material 2l', ex tending laterally to the end of the fuse to a base in which an aperture 28 in the terminal strip 2l is disposed in alignment with the screw 5 employed to secure the contact strip 4 to the block. The terminal strip 2 overlies and contacts the inwardly bent end 3 of the contact strip 4 to maire secure electrical contact therewith, the end of the block I being recessed as indicated at 29 so as to permit the terminal strip 2l to lie flush with the end of the block.

From the foregoing it will be apparent that the cable I5, with its heavy external insulation may be' inserted into the slot I6 a sufficient distance to permit the clamping of the cable to the block by means of cross bars or strips 3l), the individual conductors 'I and 20 being connected as described, to the contact strip 3, and one end of the fuse. Thus the fuse is interposed in series relation in the cable circuit and in the event of break down of the insulation on the cable I5 at its juncture with the plug then the short circuit which would occur immediately blows the fuse 22 and prevents injurious arcing or flashing.

The capacity of the fuse 22 will, of course, be chosen to conform with the load carried by the particular lamp or other apparatus connected to the cable I5, but as will be understood its capacity is relatively Small as compared to the capacity which would be required for fuses in the stationary fixed wiring system of the Stage or the setting of circuit breakers which may be a part of the fixed stage wiring system, and that the fuse 22 will readily blow out long before the effect of a short circuit at the handle of the plug could be effective to blow the high capacity fuse or to open high capacity circuit breakers.

While I have shown and described the preferred embodiment of my invention, I do not desire to be limited to any of the details illustrated or described herein, except as defined by the'appended claim.

I claim:

In a stage plug construction, the combination of a block of insulation material, a pair of ccntact terminal strips disposed along opposed sido edges of the block, a longitudinal bere formed in that end of the blocl; to be inserted into a receptacle, a cartridge fuse having a metal terminal strip connected to one of its ends and extending longitudinally beyond the end of said fuse and having a second terminal strip connected to and extending laterally from the opposite end of said fuse, whereby when said fuse is inserted in said bore, electrical connection may be made between the lateral fuse terminal strip and one of the block terminal strips and connection may be made between a conductor and the other fuse terminal strip toy dispose the fuse in series relation with a cable secured to said plug.

JULIUS H. LYTGENS.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number l Name Date 539,725 Chapman May 2l, 1895 1,513,819 John Nov. fl, 1924 658,924 Pringle Oct. 2, 1900 1,481,278 Wood Jan. 22, 11924 

